Various information processing systems have been developed with the rapid development of the information industry in recent years. In addition, methods of recording and recording equipment which are suitable for these information processing systems have been developed and put into use. Thermal transfer recording, which is one such recording method, involves the use of equipment which is light in weight and compact and which runs without noise, and which also has excellent operating and maintenance characteristics. Moreover, color recording can be achieved easily and the use of this type of equipment has become widespread in recent times.
The thermal transfer recording method includes systems in which a thermal transfer dye donating material comprising a thermo-fusible ink layer which is carried on a support is heated by means of a thermal head and the ink is fused and transferred to an image receiving material (fusion transfer systems) and systems in which a thermal transfer dye donating material which has a dye donating layer which contains a thermo-mobile dye and a binder is heated with a thermal head and recording is achieved by the thermal migration of just the dye to the image receiving layer of an image receiving material (thermo-mobile systems), generally referred to as sublimation type heat sensitive transfer systems.
This invention relates to thermal transfer dye donating materials which are used in the latter of the above mentioned thermal migration systems. Moreover, the thermo-mobile dyes referred to here are dyes which are transferred from a thermal transfer dye donating material to a thermal transfer image receiving material by sublimation or diffusion in a medium.
However, various limitations have arisen with the thermo-mobile dyes which have been used in this type of system in the past and there are very few thermo-mobile dyes which satisfy the conditions required. The conditions required are that the dye should have the preferred spectral characteristics with respect to color reproduction, that the dye should not change color or fade as a result of the action of light or heat, that there should be little denaturation due to the action of various chemicals, that there should be little or no loss of sharpness after image formation, that the image should not be liable to re-transferrence, and that the thermal transfer dye donating material should be simple to produce.
Furthermore, the light fastness of the color image may particularly decrease in an area where dyes having a different absorption wavelength are present together, resulting in a problem. Among them, the decrease of the light fastness of a cyan dye or a magenta dye, which is caused by the 10-presence of a cyan dye was particularly serious. This has not yet been made clear in detail, though it may be considered to be caused by mutual action between the different dyes, and improvements thereof have been keenly demanded.
Still further, color images of the thermo-mobile transfer mode involved a phenomenon that the light fastness remarkably decreases in a low-density area, resulting in a problem. This has not yet been made clear in detail, though it may be considered to be caused by the matter that a heat energy applied from a thermal head is not sufficient so that the dye is not thoroughly dyed into the image receiving layer. Thus, an improvement of the light fastness of the color image in a low-density area has been keenly demanded.
Among these requirements, the fact that the dyes are not liable to change in color or fade as a result of light and heat is of special importance in the case of image recording. However, the thermo-mobile dyes which have been used conventionally have been unsatisfactory in this respect, changes in color or fading have inevitably occurred in a short period of time and there has been a strong demand for improvement from the image storage point of view.
Consequently, the use of various anti-fading techniques has been suggested as a means of increasing image fastness. In one such technique, various additives which have an anti-fading action are included in the image receiving layer. Such additives include ultraviolet absorbers, auto-antioxidants, singlet oxygen quenchers, super-oxide quenchers, peroxide degrading agents and other types of stabilizers. For example, the use of ultraviolet absorbers in the image receiving layer has been disclosed in JP-A-62-260152 and JP-A-63-145089. (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".) Furthermore, the use of metal complexes has been disclosed in JP-A-1-105789 and JP-A-1-146787. The use of other light stabilizers has been disclosed, for example, in JP-A-63-74686, JP-A-63-122596, JP-A-1-127387 and JP-A-1-171887.
However, no great anti color fading effect can be achieved with the addition of compounds which have an anti-fading action to the image receiving layer.
Further, an improvement in the decrease of the light fastness of a cyan dye or a magenta dye to be present together with a yellow dye has not yet been achieved.
Still further, an improvement of the light fastness in a low-density area has not yet been achieved, too.
On the other hand, in the field of dyes in general, attempts have been made to increase the light fastness of dyes by bonding atomic groups which have the effect of inhibiting fading of the dye. Typical examples have been described in J. Appl. Chem. Biotechnol., 1977, 27, pp. 558-564.
However, there is no description or suggestion in the literature of the fact that these dyes can be used in thermo-mobile type thermal transfer applications. With the method used for thermal transfer recording in the experiments described in he literature, dyes which have been substituted with tertiary amino groups, which are supposed to have an anti-fading effect according to the results of the latest polypropylene film and polyester fiber dying experiments, in fact have a lower fastness than unsubstituted dyes.
Furthermore, the bonding of atomic groupings, which have an anti-fading action, to the couplers which are used in silver salt color photography has been disclosed, for example, in JP-A-53 82411, JP-A 55-7702, JP-A-50-20723, JP-A-59-45442, JP-A-60-222852, JP-A-61-50136, JP-A-63-24256, JP-A-1-191141, JP-A-1-186951, JP-A-1-180547, EP 178165, EP 17684, EP 117765 and U.S. Pat. No. 3,519,429.
However, the couplers which are used in silver salt color photography mentioned above are designed in such a way as not to diffuse from the film of the photosensitive material during the course of the operations of development processing. On the other hand, the dyes which are used in the thermo-type of thermal transfer are such that the dyes are transferred directly by sublimation or thermal diffusion on the application of heat. Hence, unless the thermo-mobility of a dye is very high it is impossible to obtain satisfactory image densities and it cannot be used to form thermal transfer images.
Thus, the design concept for couplers which are to be used in silver salt color photography and the dyes originating therefrom are incompatible with the design concept for the dyes which are used in thermal migration type thermal transfer materials. It is to be expected that the couplers which are used in silver salt color photography and the dyes derived therefrom will not be usable in thermo-mobile dye type thermal transfer recording.
In addition, it is unpredictable from the above-cited conventional techniques that a color image formed from the thermal dye donating material of this invention exhibits extremely high fastness even in a gray area or hardly causes a reduction of the fastness even in a low-density area.
Furthermore, JP-A-63-246285, JP-A-63-246286 and JP-A-64-77584 disclose anthraquinone dyes substituted with an alkoxyphenoxy group.
However, since in these anthraquinone dyes the alkoxyphenoxy group is directly conjugated with a dye-.pi. conjugation system, the alkoxyphenoxy group constitutes a part of the color forming system and does not inherently have the effect of suppressing the fading. Therefore, these patents are irrelevant to the subject matter of this invention.
In detail, the subject matter of this invention is to suppress the fading more effectively by bonding an atomic grouping which inherently has the effect of suppressing the fading to a dye moiety via a connecting group. Examples of the effects which are brought by suppressing the fading include ultraviolet light absorption action, automatic anti-oxidant action, singlet oxygen extinction action, superoxide extinction action, peroxide decomposition action, and radical trapping action as well as light stabilization action (e.g., extinction action in the dye excited state by electron transfer or energy transfer).
The atomic groupings are required to have a special structure meeting the respective actions. However, if an unnecessary substituent group is introduced, its effect disappears. The above-described alkoxyphenoxy group of the anthraquinone dye is directly conjugated with a dye-.pi. conjugation system and, therefore, an ability of the alkoxyphenoxy group to disappears. This is evident from a phenomenon that the electron transfer or energy transfer takes place between at least two independent systems.